• Preheat the oven to 180'C (170'C fan) / Gas 4. Fill a 12-hole baking tin with cupcake cases and set aside while you make the cake batter.
• Add the butter, sugar and orange extract to a large mixing bowl and beat with an electric whisk until pale and creamy.
• Crack the eggs into the mixing bowl and beat again for 30 seconds to combine. Scrape down the sides of the bowl using a spatula.
• Sift in the self-raising gluten free flour, cocoa powder and xantham gum, add the milk, and then beat together with the electric whisk until everything is fully combined. You want a fairly thick batter which looks light and fluffy. Fold in the chocolate pieces until evenly distributed through the mix.
• Spoon the mixture evenly between the cupcake cases and then place in the centre of an oven and bake for 20-22 minutes. The cupcakes are done when they are well-risen, golden on top, and a skewer inserted in the middle comes out clean.
• Once cooked, remove from the oven and place on a cooling rack. Cool in the tray for 10 minutes before removing the cakes from the tray to cool completely.

To make the frosting:

• Add the butter, icing sugar, milk, melted chocolate and orange extract to a large mixing bowl and beat with an electric whisk on a low speed until it becomes a smooth, pale buttercream.
• Spoon the mixture into a piping bag (see notes) and, once the cupcakes are completely cool, decorate them with a swirl of buttercream. Finish with orange zest on top.